DESCRIPTION: (Adapted from the Applicant's Abstract.) The objective is to evaluate the adaptability of the motor system to environmental demands, such as the force of gravity, and the mechanisms underlying neuronal plasticity. Behavioral, electromyographic and molecular approaches will be used to study rat pups from postnatal day 6 through 31 in ground and flight based experiments. Behavioral measures will assess the development of interlimb coordination, dynamic postural stability, and complex motor skills. Electromyographic recordings of activity from hindlimb muscles will be combined with video-based motion analysis of treadmill walking to examine the neuronal basis for locomotion in control and experimental animals. Biochemical and immunohistological studies will determine the pattern of expression of glutamate receptor subunits genes in the lumbar spinal cord. Both the "sensitive" and the "critical" period of motor development will be assessed by examining rat pups reared aboard the shuttle at different postnatal periods. Since the major elements of the motor system - neurons, muscles, and bone - will develop under the condition of microgravity, the proposed experiments will further our understanding of the plasticity and interaction of these systems during postnatal development and in adult motor function.